IT is said that behind every great man is a great woman. But who knew that behind seemingly every teenage girl on television is a little-known, mild-mannered man?

Scan the credits of a prime-time television drama series with a teenage girl protagonist and you’re bound to see the name Leslie Morgenstein, chief executive of Alloy Entertainment. He may not have his own Wikipedia entry, but over the last 10 years he has transformed Alloy, which packages teenage book series like “Sweet Valley High” and “Sisterhood of the Traveling Pants,” into a prolific producer of television series adapted from the company’s books.

“One of the things we do really well as a company is identifying properties in our library that are right for our time,” said Mr. Morgenstein, who has overseen the revival of once-dormant book titles like "The Nine Lives of Chloe King" and “The Secret Circle” as new television series. As television shows, “Gossip Girl,” “The Vampire Diaries” and “Pretty Little Liars” have captivated the elusive 12- to 34-year-old female demographic with a combination of mystery, high-stakes romance, luxe lifestyles and, often, a touch of the supernatural. (The cultural impact of “Gossip Girl” has long surpassed its mediocre ratings. Online buzz and Internet viewing, increasingly the gauges by which shows are measured in this demographic, were high for the show, now coasting a bit on its former glory as it heads into its fifth season.)

Three series having their debuts this month and next will bring Alloy’s roster to six, making it one of the fastest-growing production companies creating shows for networks and cable (known in industry parlance as “pods”). “They have their finger on the pulse of the millennial audience,” said Michael Riley, president of ABC Family, which broadcasts Alloy’s “Pretty Little Liars” and two of its latest shows, “The Nine Lives of Chloe King” and “The Lying Game.” (The third, “The Secret Circle,” will have its premiere on CW in September.)

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Skyler Samuels, the title character in “The Nine Lives of Chloe King.”Credit
Bruce Birmelin/ABC Family

Despite his abundant output, Mr. Morgenstein, 44, maintains a low profile in Hollywood. So much so that Gina Girolamo, his senior vice president for television, didn’t know that her future boss was a man until they met last year. “I thought Leslie Morgenstein was a lady, based on the credits of my favorite shows, ‘Gossip Girl’ and ‘Vampire Diaries,’ ” Ms. Girolamo, a former NBC executive, said.

Regardless, Mr. Morgenstein, a married father of two sons who is based in New York, seems to know what girls want. “Because we are middle-aged Jewish guys,” he said of the company’s management team, “we hire a lot of creatives who are young women, who are much closer to the audience.”

Drinking coffee in a hotel lobby on a recent visit to Los Angeles, he described his company as “research shy,” an unusual quality in an industry obsessed with trend tracking and focus-group testing. Alloy executives prefer to rely on the instincts of a team of editors, development executives and writers who already know this audience. “Either you have a nose for commercial material, or you don’t,” Mr. Morgenstein said.

One writer who does is Dan Berendsen, a veteran of the teenager and tween market, who adapted Alloy’s “Nine Lives of Chloe King” for television. It’s the story of a high school girl with catlike superpowers who must fight in a war between humans and an ancient race of which she has just learned she is a descendant. There are three novels in the series, which began in 2004; Mr. Berendsen said he used up the books’ story lines in the show’s pilot episode.

“We’re allowed to come up with our stories,” he explained. “Alloy has been supportive and hands-off.”

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Leslie Morgenstein, the chief executive of Alloy Entertainment.Credit
Chester Higgins Jr./The New York Times

Until the last few years, many executives looked down on the teenage-girl demographic, Mr. Berendsen added. “They had an idealized vision of what they thought a teen girl might like. It was usually a little too sweet.”

All assumptions of sweetness were dispelled once the “Twilight” books and movies demonstrated the supernatural genre’s female appeal. But Alloy had already done its own vampires-in-high-school, forbidden-romance book series, “The Vampire Diaries,” in 1991, and the “Twilight” phenomenon led the company to reissue the four original “Vampire Diaries” novels. Those were soon followed by two more trilogies and a TV version, which begins its third season on CW next month.

Mr. Morgenstein grew up in Chevy Chase, Md., and received a master’s degree in creative writing from City University of New York, but he soon realized his true talents were in steering other people’s creative ideas. So he pursued an M.B.A. at New York University. But, as Ms. Girolamo said, he’s still a writer at heart. “The beauty of the way his brain works is he’s all about storytelling,” she said.

Mr. Morgenstein started at the company after he graduated college, when it was known as Daniel Weiss Associates. Over the years, as Daniel Weiss Associates became 17th Street and then Alloy, Mr. Morgenstein attended business school at night and realized that TV and movie adaptations would be a lucrative business. But they were Hollywood outsiders. “It took a while, but we have, for now, figured it out,” he said.

The company dived into the adaptation business with the successful movie version of “The Sisterhood of the Traveling Pants” in 2005. (It grossed a modest $39 million at the box office, and its 2008 sequel earned nearly $45 million.) “Gossip Girl” kicked off its work on television in 2007. Mr. Morgenstein’s sons, ages 12 and 15, do not watch “Gossip Girl,” but they are, he said, “New York City kids.” In other words, they’re media savvy, and they tip off their father to cultural trends. The older son has seen at least one Alloy adaptation: “Sex Drive,” the company’s anomalous 2008 feature in which a high school boy drives across the country to have sex with a girl he met online. Mr. Morgenstein considers it a rare misstep.

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Covers of the books that Alloy Entertainment has turned into television series.

The Alloy formula has been the subject of criticism. The company hires a writer to execute a series, often under a pen name. Story creation is a collaboration among executives and the writer, who cedes ownership of the results to Alloy. It’s a factorylike methodology that runs contrary to the view of a writer as a work’s supreme creator. But the Alloy way is pretty much how it works in television, where one person’s singular vision is the exception and a writer-for-hire relationship is the norm.

“We’re not precious about the details,” Ms. Girolamo said of the television-development process. “That way each project can be specific to where we want to try to sell it.” In the case of “The Lying Game,” which drew 1.4 million viewers for its premiere on Aug. 15, the book series and its on-screen version diverge dramatically. The story is about long-lost twins, one a foster child, the other adopted by a wealthy family, who essentially swap places. On TV they’re both alive; in the books one of them is narrating from the dead.

“We felt that for the TV series we wanted to see both sides of it,” Mr. Morgenstein said. “Also it’s very dark and potentially not relatable to have the main girl posing as her dead sister.” As Alloy continues to scramble the which-came-first process of creating books and television, the company is becoming increasingly platform agnostic. “Pretty Little Liars,” the hit series (it has an average of 2.1 million viewers) about a mysteriously dead girl and the clique she left behind, was developed simultaneously for the page and the screen. The television development took so long that the eighth book in the series was coming out as the first episode came on.

The company’s next series, “How to Rock,” coming to Nickelodeon in 2012, represents many firsts. It’s Alloy’s first show on the kids’ channel, its first half-hour comedy, its first musical and its first project to be set up on TV before being developed as a book. (Titled “How to Rock Braces and Glasses,” the book comes out in October.)

“ ‘How to Rock’ was really strategic for us, like, how do we expand?” Mr. Morgenstein said. The answer: carefully. “We’re not going to go from ‘Pretty Little Liars’ to ‘NCIS.’ ”

Correction: September 4, 2011

An article last Sunday about Alloy Entertainment, creator of many television shows aimed at teenage girls, erroneously included one book among the once-dormant book titles Alloy has turned into TV series. While Alloy did so with “The Nine Lives of Chloe King” and “The Secret Circle,” “The Lying Game” was not a dormant title. The article also misstated the age of the younger son of Leslie Morgenstein, Alloy’s chief executive. He is 12, not 11.

A version of this article appears in print on August 28, 2011, on Page AR14 of the New York edition with the headline: His Finger on the Pulse Of What Girls Watch. Order Reprints|Today's Paper|Subscribe